Engine breathless at higher throttle openings

Sorry, i'm sure this problem has been posted before...but when I open up
the throttle more than just a little bit, the engine wheezes and the
bike slows down. I can only get the bike up to about 40 mph.

The bike also makes some clatter when it's idling...maybe valve clearance?

I just bought the bike, a 1984 KZ700 with 8500 miles. The carbs are
definitely sketchy and I plan on opening them up but I wanted to have an
idea what to look for before I went in.

Thanks for advice! It's always appreciated.

 

Plan on going through the fuel system and the air intake system and
cleaning it all out.

Dirty or old gasoline in the tank. Dirty petcock with fouled fuel
filter. Fuel float valve dirty, float stuck. Plugged up idle jets and
idle passages. Really dirty or oil-fouled air filter. Install new spark
plugs too.

Maybe. The clutch basket will rattle until you pull the clutch lever
in. The starter clutch won't stop rattling. It's under the cover on the
left hand end of the engine.

Problem could also be a loose cam chain, check the tensioner and check
the valve clearances.

Same game as before. Look for the EPA anti-tamper plugs and see if
they've already been drilled out. If not, you'll probably have to do it
anyway to remove the idle mixture screws so you can spritz the idle
passages out.

 

Sounds like the diaphragms, assuming it's CV carbs (sounds about right).
When you take the carbs apart to clean them out (another thing you need
to do), check the vacuum diaphragms for tears or holes.

All Kawasaki in-line fours of that era make some clatter while idling.
The cam chain is the typical culprit, but the valves clatter too if set
to the best place for assuring good cam wear (towards the loose end of
the spec). I suspect you have nothing wrong other than typical Kawasaki
noise, I've never had a Kawasaki that didn't sound like a freakin'
diesel at idle what with all rattling chains and clattering valves.

Do check the valve clearance. Also check the cam chain guides at the
same time. If (when) the cam chain guides wear out, the chain rubs
directly against metal, making a horrible racket, but on a bike with so
few miles that's unlikely. Also check to make sure that the cam chain
tensioner is working okay. I don't recall whether Kawasakis of that era
had a ratchet tensioner or a manual one, find a service manual. If it
has a manual tensioner, adjust it. If it has a ratchet tensioner, take
out the spring (the center bolt on the thingy), pull the tensioner,
check that it works (push the spring in and watch to see that the "foot"
sticks out and won't ratchet back in), then reset it to full in and
re-install. Then push the ratchet with a skinny screwdriver or such
until you feel it push against the chain guide and make one final
"click", then re-install the spring. (Springs get old too, and may not
make that final "click"). That final "click" tends to quieten the chain
down to reasonable levels, though Kawasaki engines of that era will
never be accused of being smooth -- they were crude, noisy, and
rough-idling beasts with the redeeming quality of also being simple
well-proven technology that even today is relatively easy to maintain.

You're welcome!

- Elron

 

Do all the exhaust pipes come to about the same temperature?

Check the compression and the plug in each cylinder.

 

Check for missing airfilter or airfilter housing leaks on the filtered
side(goes lean and will try to stall like you are describing).

J.

 

The bike is actually running with the filter and filter pipes removed.
If this were the case, would running with the choke on make it run
slightly better?

 

In short, yes!

J.

 

Probably not, your carburetors most likely don't actually have a choke
plate. Some slide valve carburetors used on the Kawasaki KZ650 in the
mid-1970's did have a real choke like a car. When you close the choke
plate, it makes the carbs suck harder and more gas gets pulled out of
the float bowls. But, with a constant vacuum carburetor, there is
usually no choke plate. There is a bypass passage around the butterfly.
And that passage is a lot smaller than the open area in the carburetor
throat when you open the throttle butterflies. So no extra fuel gets
sucked into the engine when you use the newer type of choke, which is
called a "starter".

 

And how do you think this starter circuit works? By letting more
gasoline into the carb/intake, fattening up the mixture. Same function,
different principle.

J.

 

I know exactly how it works. There's a plunger (also called a
"starter") in a bypass passage that goes around the closed butterfly. A
rather large jet (about 0.6 mm orifice size) in the float bowl supplies
gasoline. The mixture drawn through the starting enrichener can be as
rich as 1 to 1.

But, as soon as you open the throttle, vacuum drops off to the point
that NOTHING gets sucked through the enrichener bypass.

This can be demonstrated by the fact that the engine will quit if the
pilot jets are plugged up. If the starting enrichener was capable of
keeping the engine running with such a rich mixture as 1 to 1, why
would it even need the tiny amount of gasoline that would come through
an idle jet that is 0.35mm to 0.45mm orifice diameter?

If the enrichener worked like you think it does, it would continue to
supply enough mixture to keep the engine running with plugged idle jets
when you open the throttle.

Go ride your motorcycle and see what happens when you're operating at a
large throttle opening. You won't notice any difference in engine
operation the way you would with a plate type choke.

When you slow down and stop, the engine will run a little rough though,
with the throttle closed.

 

This is not correct, it would not be possible to run a bike on a cold
morning if the enrichment circuit dropped off as soon as you opened the
throttle, try and see!!

I was working today with this exact problem! 50cc four-stroke Vespa,
plunger type cold start circuit(automatic via bi-metal and heat coil).

Place it outside in the cold and you are barely able to start
it(Accelerator pump lets you), try to drive away and it does 2Mph and
sputters till it warms up.

This proves that the starter circuit does indeed fatten up the mixture
even as you open the throttle.

But hey, I@m not here to argue, believe what you want....

Jørn Berg. In Norway.

 

If you have to open the throttle to start the engine with the starting
enrichener valve fully open, the idle mixture screws are set too lean,
or the idle jets are plugged up. An engine with constant vacuum carb is
particularly difficult to start by twisting the throttle because the
starter won't spin the engine fast enough to crank up very much vacuum.

Some of what little vacuum it does make at cranking speeds is needed to
open the automatic petcock. That's something else that confuses
newbies. Engine won't start after the motorbike hasn't been ridden for
a few weeks, even though he has gas in the tank.

But we weren't talking about a 50cc Vespa, we were talking about a
Kawasaki 700cc
I-4.

That's what you say. The usual routine in this NG is that somebody who
doesn't know much can't get his machine running right. So he posts a
query on rec.motorcycles.tech. Then somebody answers him. Then somebody
else who likes to argue tells the first respondant that he doesn't know
what he's talking about.

Let me point out something about the starting enrichener that you may
not have noticed. The bypass is around 1/4 of an inch in diameter. It's
pretty much straight. There's no room in the bypass for much of a
venturi, so there isn't very much pressure diferential to suck fuel out
of the float bowl. The engine has to suck air through what is basically
about the size of a straw. That's why the starting enrichener quits
working when you turn the throttle grip. Not enough vacuum to suck the
gas up.

 

I opened up the carbs yesterday, they looked ok. I was concerned that it
was getting *too much* fuel instead of not enough before but this
doesn't seem to be the case...
So running the bike without the air filter and filter pipes could cause
the problem I am having, to this severity? I never thought it made such
a large difference.

 

Oh, and if it makes any difference...when the engine is warm and I pull
the choke, the RPM's jump to about 5000(!)

 

One last thing - I did check compression, it's good (150 psi) and the
spark plugs are clean.

The diaphragms seemed alright from what I could tell (pushing them up
with my finger, plugging the port, and releasing them - they all came
down pretty slowly) and the two I can see while the engine is running do
respond to throttle inputs.

 

Have the EPA anti-tamper plugs been drilled out yet? If you can see the
slotted heads of the idle mixture screws, they've already been monkied
with.

The mistake a lot of shade tree mechanics get into is that they expect
the engine idle speed to increase as they turn the idle mixture screws
counterclockwise. The engine speed increases to a point, and then
actually starts slowing down.

So the shade tree mechanic turns the master idle knob to make the
engine idle faster.
And the idle RPM runs away when the engine is hot. The idle RPM will
also be too high when the engine is on the choke when it's cold in the
morning.

If you can't see the idle mixture screws, the EPA plugs are still in
there and my diagnosis is that your idle mixture passages are all
plugged up and the engine gets fuel from the starting enrichener
("choke") when you open the throttle a lot, but the engine falters and
stalls at smaller throttle openings.

Been there, had that problem. Fixed it by cleaning the carbs with
Berryman's B-12 Chemtool Chose and Carburetor Cleaner in the aerosol
can.

You can open up the carbs and clean out the pilot jets and still have
idle mixture passages full of gum and varnish if yuo don't know how the
idle mixture passage goes four different ways.

With the anti-tamper plugs drilled out and the idle mixture screws
removed (1), you can squirt Berryman's B-12 through the hole the idle
mixture screw came out of and the
carb cleaner must squirt out four different ways.

1. It must come out the hole closest to the idle mixture screw.

2. It must come out the three holes next to the throttle butterfly.

3. It must come out the pilot jet.

4. It must come out the pilot air jet in the intake bell.

Since you don't have a lot of pressure out of an aerosol spray can, you
can hold your fingers over some of the holes while you are spraying
carb cleaner through any of the holes.

(1) Count the number of turns it takes to lightly seat the idle mixture
screws in the bottom of the hole. Write those numbers down on a piece
of paper. When you reinstall the screws, make sure you get each screw
back into the hole it came out of.

All four screws should probably be around 1/4th to 1/2 a turn open,
unless your carbs have extremely small pilot jets.

With CV carbs, turning the screw clockwise leans the mixture up.
Turning the screw counterclockwise richens the mixture up. What you are
trying to do when adjusting the screws with the engine running is to
get the engine to just start running rough as you turn the idle mixture
screw clockwise. Then you can turn the screw back counterclockwise
about 1/8th to 1/4th of a turn to get the engine to run smoothly again.

 

The tamper plugs are intact.

I don't fully understand this...because the bike idles fine when the
starter circuit is off at around 1000 RPM, but even when the bike is
warm it will rev wayyy up when the starter circuit is enabled. Won't a
correctly operating bike slow down in this condition, or even stall?

I thought the bike would be running way too lean, and that the richer
starter mixture was closer to optimal and this is why the bike would
speed up so much.

Again, the air filter and piping is completely disconnected, would this
alone cause the problem I am having or does it sound like there is
something else at work here?

I did run cleaner through it, although I will admit I was not this
thorough. The carbs will surely be out again soon, and I will do this.

I had this experience with my KZ750 twin...oh god, what a nightmare.
Hopefully it was just a weak spark after all.

Thanks for the response, always appreciated.

 

If the airfilter setup is missing and the carbs have NOT been
re-calibrated with larger mains(might also need larger idle jets), it
will stumble/hesitate like you describe.

J.

 

I'm sorry. I forgot that Kawasaki put a fast idle mechanism on the
right hand end of the
shaft that opens the starting enrichener valves. On a car, the fast
idle mechanism will have some sort of dashpot rigged to a heat
controlled choke plate, but this mechanism is stupid, it just blocks
the throttle open a little bit while the choke is on, making Kawasaki
engines run away whether hot or cold.

TOG knows about this, I'm surprised he didn't catch it.

Go to www.partsfish.com and look at the Carburetor Assembly 1 2 drawing
and you will see"

13168 LEVER,CHOCK
16041 SHAFT-CARBURETOR,CHOC
92022 WASHER,SPRING
92033 RING-SNAP,E
92045 BALL,STEEL,1/8"
92081A SPRING,FAST IDLE SHFT
39184A BRACKET-ASSY,THROTTLE

 

X

Put the airfilter back, it's there for a reason
The dust particles are going to cause extra wear to the engine